Along with fast development of mobile network and highly competition in the market, it is one of important manners to raise service by providing diverse and multiple level services. Mobile prepaid service is one of new services. It is not only welcomed by subscribers, but also has many advantages for operator, such as increasing profit, expanding market share, getting telephone fee in advance and avoiding bad debt etc. The so-called mobile prepaid service is: after a mobile telephone subscriber opens an account, he (she) purchases rechargeable card with fixed amount of face value to recharge his (her) account. When making a call, connect or disconnect the call depends on account balance. The balance in the account is calculated in real-time while the call is going on. When balance in the account is spent out, the call is disconnected. In this way, subscriber implements prepaid function for call and other services.
Intelligent network, which creates new services rapidly and effectively, is one kind of the “value-added” network, which is characterized of creating new service rapidly and loading upgrade service dynamically. Therefore, as intelligent network is rapid, convenient, flexible, economic and effective for creating and implementing various new services based on the existing mobile network, it is an effective manner to support prepaid service and other mobile intelligent service.
Intelligent network includes mainly following entities: service switching point (SSP), service control point (SCP), service data point (SDP), service management point (SMP), service management access point (SMAP) and intelligent peripheral (IP) etc. SSP performs mainly separating switching and service. It detects an intelligent call and processes it with SCP interactively. SCP executes service logic for the intelligent call detected by SSP and instructs SSP to execute corresponding call control, such as operations of connect, release etc. SMP performs mainly service management and subscriber management. SMAP is mainly used for SMP and SCP data access. IP provides mainly voice operation, receiving number and voice synthesis etc., usually IP is integrated in SSP called SSP/IP.
SDP is an important part of intelligent network. It stores data of intelligent network and includes service data function (SDF). In ITU-T Q.122x series recommendations, SCP and SDP interconnection interface protocol is defined, SCF-SDF interface specification is described in detail. SDF is acronym of Service Data Function, means function of service data. Acting as an interface of service logic and service database, sometimes, SDF function is abstracted as SDP entity. Usually, SCP includes service control function (SCF) and SDF function, and provides access database service to other SCP, through SCF-SDF interface.
Along with gradually expansion of prepaid service, subscribers of the service increase continuously. From the security point of view, it can not store too many subscriber data in single SCP. Thus, a mobile intelligent network with large capacity has many SCPs. Prepaid service subscribers of different locations are distributed to corresponding SCPs. According to present technology, usually, SDP is set in SCP. Therefore, after setting up many SCPs, rechargeable card data are distributed to each individual SCP accordingly. For example, suppose prepaid subscriber of location A roams to location B and purchases a rechargeable card of location B for prepaid purpose. As the subscriber data is in the SCP of location A, and rechargeable card data is in the SCP of location B, so the SCP of location A wants to query and update rechargeable card information in the SCP of location B. Under this mode, any two SCPs need to be interconnected, and network topology is mesh network architecture. This is complicated and difficult for setting up a network and engineering implementation. In addition, as the rechargeable card data are distributed, complication is increased for engineering, data management and statistic.